of the four you mention, hitch.. i could see 1 happening:

"Eliminating x, y, z federal agencies/departments? Not going to happen."

This is probably one of the few that could happen. A president simply doesn't appoint anyone to take over a department and it's pretty much shuttered.. .Or he merges it into another dept.

"Repealing the ACA? Not going to happen. "

It's why Romney never ran on immediately getting rid of the ACA.. he ran on the voucher process for opting out as his first statement.

Eliminating the tax code and starting over? Not going to happen.

I'm trying to decide if this _could_ happen or not.. Revamp? Possibly, complete elimination/rewrite.. agreed won't happen.

Passing a Constitutional Amendment for a social issue? Not going to happen.

Total agreement.. Ironically, that gets away from what most conservative voters (IMO) want.

I disagree with you on the Planned Parenthood issue though.. that was not a "we'll make up to voters for failing on.. (insert voting issue here}." The moment those various stories/videos hit the airwaves, you knew something was going to have to happen, and it wasn't just on the religious right arm of the GOP; it was on Catholic Dems voters as well.